The prior art focusing actuator of a voice coil motor has a retainer and a lens cylinder movably installed to the retainer. The structure of this prior art actuator has a complicated structure. Thereby the sealing of the structure is not better so that undesired objects, such as dusts, will enter into the structure.
In one improvement structure, the retainer is formed by a plastic retaining frame to enclose a metal structure. The retainer has four magnets as a fixed structure for receiving a movable structure formed by a lens cylinder and coils. A resilient spring is installed between the fixed structure and the movable structure. Then the fixed structure is assembled within a support box. Thus a focusing actuator of a voice coil motor is formed.
However, the above mentioned actuator can resolve the problem in the prior art, but since the retainer is formed by a plastic retaining frame to enclose a metal structure. A periphery of the retainer is an insulated frame. The four magnets are not well connected so that magnetic flux will leak out and thus the magnetic flux circuit can not be well operated.
Moreover, the manufacturing process of the prior art is complicated. The retainer is made by two different materials. It is difficult to combine the two different materials. Thus the stability of the retainer is not good. As a result, the magnetic flux loop is not perfect so as to affect the efficiency of the magnetic flux.